J. Am. Chem. SOC.1992, 114, 4351-4364
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Complexes between Formaldehyde and Titanium Tetrachloride. An ab Initio Study Vicenq Branchadell* and Antonio Bliva* Contribution from the Departament de Quimica. Universitat Autonoma de Barcelona, 081 93 Bellaterra, Spain. Received June 13, 1991
Abstract: The complexes of titanium tetrachloride with one or two molecules of formaldehyde have been studied with ab initio SCF-MO methods. Several structures of the H2C0-TiC14, (H2C0)2-TiC14,and (H2CO-TiC14)2complexes have been considered, and the rearrangements between them have been discussed. The interaction between formaldehyde and TiCI4has been analyzed in terms of molecular orbital interactions, and the effects produced by complex formation have been rationalized.
Introduction Complexation of carbonyl compounds by Lewis acids plays an important role in many catalytic processes in organic chemistry. These include catalyzed Diels-Alder reactions,' aldol condensat i o q 2 and several photochemical reactions., The drastic effects that the activation by Lewis acids produces in the mechanism of these reactions make the knowledge of the structure and properties of such complexes necessary. In the last years, several experimental studies have shown that complexation by Lewis acids produces important modifications on UV,3c94IR,435 and NMR3c,d.6*7 spectra of carbonyl compounds. Crystal structures have also been determined for several complexes, showing a bent coordination mode of the carbonyl compound.8 Boron and aluminum trihalides only form 1:1 complexes with carbonyl compounds. However, other Lewis acids such as TiC14 or SnC14 also form 2:l complexes, through coordination of two different carbonyl compound molecules, and chelates with bidentate carbonyl compounds, so that a six-coordinate complex is obtained. This chelating ability seems to play an important role in the diastereofacial selectivity of reactions involving chiral carbonyl compound^.^ In the case of TiCI4, complexes with chelating esters and complexes of dimeric TiC14 have been reported.'O ( I ) (a) Yates, P.; Eaton, P. J . Am. Chem. SOC.1960.82, 4436-4437. (b) Lutz, E. F.; Bayley, G. M. J . A m . Chem. Sor. 1964, 86, 3899-3901. (c) Sauer, J.; Kredel, J . Tetrahedron Left. 1966, 731-736. (d) Inukai, T.; Kojima, T. J . Org. Chem. 1966, 31, 1121-1123. (e) Inukai, T.; Kojima, T. J . Org. Chem. 1966,31,2032-2033. (f) Inukai, T.; Kojima, T. J . Org. Chem. 1967, 32,872-875. (8) Williamson, K. L.; Li Hsu, Y. F. J . Am. Chem. SOC.1970, 92, 7385-7389. (h) Kakushima, M.; Espinosa, J.; Valenta, Z. Can. J . Chem. 1976, 54, 3304-3306. (i) Lindsay Smith, J. R.; Norman, R. 0. C.; Stillings, M. R. Tetrahedron 1978, 34, 1381-1383. 6 ) Bonnesen, P. V.; Pucket, C. L.; Honeychuck, R. V.; Hersh, W. H. J. Am. Chem. SOC.1989, I l l , 6070-6081. (k) Narasaka, K.; Iwasawa, N.; Inoue, M.; Yamada, T.; Nakushima, M.; Sugimori, J . J . A m . Chem. SOC.1989, I l l , 5340-5345. (2) (a) Mukaiyama, T. Angew. Chem., Int. Ed. Engl. 1977, 16, 817-826. (b) Yamamoto, Y. Acc. Chem. Res. 1987, 20, 243-249. (3) (a) Lewis, F. D.; Howard, D. K.; Oxman, J. D. J . A m . Chem. SOC. 1983, 105, 3344-3345. (b) Lewis, F. D.; Oxman, J. D.; Huffman, J . C. J . Am. Chem. Soc. 1984,106,466468, (c) Lewis, F. D.; Oxman, J. D.; Gibson, L. L.; Hampsch, H. L.; Quillen, S. L. J . Am. Chem. SOC.1986, 108, 3005-301 5. (d) Lewis, F. D.; Howard, D. K.; Oxman, J. D.; Upthagrove, A. L.; Quillen, S. L. J . A m . Chem. SOC.1986, 108, 5964-5968. (e) Lewis, F. D.; Quillen, S. L.; Hale, P. D.; Oxman, J . D. J. Am. Chem. SOC.1988, 110, 1261-1267. (f) Lewis, F. D.;Barancyck, S. V. J . Am. Chem. SOC.1989, I l l , 8653-8661, (4) Rabinovitz, M.; Grinvald, A. J . Am. Chem. SOC.1972, 94, 2724-2729. (5) Chewier, B.; Weiss, R. Angew. Chem. 1974, 86, 12-21. (6) Childs, R. F.; Lindsay Mulholland, D.; Nixon, A. Can. J. Chem. 1982, 60, 801-808. (7) Hartman, J. S.; Stilbs, P.; Forsen, S. Tetrahedron Left. 1975, 3497-3500. ( 8 ) Shambayati, S.; Crowe, N. E.; Schreiber, S. L. Angew. Chem., Inf. Ed. Engl. 1990, 29, 256-272 and references cited therein. (9) Reetz, M. T. Angew. Chem., Inf. Ed. Engl. 1984, 23, 556-569. (IO) (a) Bassi, I. W.; Calcaterra, M.; Intrito, R. J . Organomet. Chem. 1977, 127, 305-313. (b) Poll, T.; Metter, J. 0.;Helmchen, G. Angew. Chem., I n ! . Ed. Engl. 1985, 24, 112-114. (c) Utko, J.; Sobota, P.; Lis, J . J . Organomet. Chem. 1987, 334, 341-345. (d) Sobota, P.; Utko, J.; Lis, T. J . Organomet. Chem. 1990, 393, 349-358.
Scheme I
+
i
H2C0
TiCI4
2.
H2CO-TiCI4 + H 2 C 0
3.
2 H2CO-TiCI4
H2CO-TiCI4
-
(H2C0)2-TiC14 ( H2CO-TiCI 4)2
Complexes between Lewis acids and carbonyl compounds have also been the object of theoretical studies."-20 Complexes with boron trifluoride have been studied by means of semie m p i r i ~ a l ' ~ ~as' ~well ~ ~as ~ ~a b' *initio m e t h o d ~ . ' ~ - 'All ~ Jthese ~~~~ studies show a preference for a bent coordination mode of BF3, in good agreement with the X-ray diffraction structure of the benzaldehyde-BF, complex.I3 Complexes of formaldehyde with BF,, BCI,, and BBr, have been studied recently by us,2oand the interaction scheme between the donor and acceptor moieties has been analyzed from molecular orbital considerations. This analysis has permitted us to rationalize the effects produced by complexation on the structure and properties of formaldehyde as well as the Lewis acidity scale of boron trihalides. Transition metal complexes of formaldehyde have also been studied t h e ~ r e t i c a l l y . ~However, ~ only complexes with electron-rich metals have been considered. For these kinds of complexes, the formaldehyde molecule is generally q2 coordinated and the main interaction between the metal and formaldehyde is the *-back donation from the transition metal to the ligand. The purpose of the present paper is to extend our study of the formaldehyde-lewis acid complexesZoto the early transition metal halide TiC14. We have considered both 1:l and 2:l complexes, the different structures of these complexes, and the interconversion between them. The formation of complexes of dimeric TIC4 has also been discussed. The nature of the interaction between formaldehyde and TiC14 and its effect in the formaldehyde molecule have been analyzed. (11) Castro, E. A.; Sorarrain, 0. M. Theor. Chim. Acta 1973, 28, 209-2 12. (12) Raber, D. J.; Raber, N. K.; Chandrasekhar, J.; Schleyer, P. v. R. Inorg. Chem. 1984, 23, 4076-4080. (13) Reetz, M. T.; Hiillmann, M.; Massa, W.; Berger, S.; Rademacher, P.; Heymans, P. J . A m . Chem. SOC.1986, 108, 2405-2408. (14) Nelson, D. J. J . Org. Chem. 1986, 51, 3185-3186. (15) Loncharich, R. J.; Schwartz, T. R. M.; Houk, K. N. J . Am. Chem. SOC.1987, 109, 14-23. (16) Guner, 0.F.; Ottenbrite, R. M.; Shillady, D. D.; Alston, P. V. J. Org. Chem. 1987, 52, 391-394. (17) LePage, T. J.; Wiberg, K. B. J . Am. Chem. SOC.1988, 110, 6642-6650. (18) Laszlo, P.;Teston, M. J . Am. Chem. SOC.1990, 112, 8750-8754. (19) Gung, B. W. Tefrahedron Lett. 1991, 32, 2867-2870. (20) Branchadell, V.; Oliva, A. J . Am. Chem. SOC.1991,113,4132-4136. (21) (a) Sakaki, S.; Kitaura, K.; Morokuma, K.; Ohkubo, K. Inorg. Chem. 1983, 22, 104-108. (b) Rosi, M.; Sgamellotti, A,; Tarantelli, F.; Floriani, C. Inorg. Chem. 1988, 27, 69-73. (c) Rosi, M.; Sgamellotti, A,; Tarantelli, F.; Floriani, C.; Guest, M. F. J . Chem. Soc., Dalton Trans. 1988, 321-327. (d) Versluis, L.; Ziegler, T. J . A m . Chem. SOC.1990, 112, 6763-6768.
0002-7863/92/1514-4357$03.00/00 1992 American Chemical Society
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J . Am, Chem. SOC..Vol. 114. No. 11, 1992
Branchadell and Oliua
Table I. Computed Energies" for H 2 C 0 , TICI,, and H2CO-TiC14 level of calculation molecule
structure
HF/HWl -1 13.221 820 -62.370 113
HF/HW2 -113.221 820 -62.374 256
HF/3-21G -113.221 820 -2673.744 386
HF/MIDI-3 -113.176999 -2674.223 295
HFIDZ -113.830448 -2686.423 342
MP3lDZ -114.038 126 -2686.716 994
A1 A2 A3 A4 El E2 E3
-175.625 163 -175.622772 -175.622 348
-175.628 028 -175.623 550 -175.622 982
-2787.440 349
-2800.283 660
-2800.776 926
-175.615356 -175.607 170 -175.612448
-175.615559 -175.606 804 -175.612058
-2787.008 575 -2787.006 309 -2787.005 957 -2787.005 839 -2786.999651 -2786.991 673 -2786.996 385
-2787.424 351
-2800.146 966
H2CO TiCI4 H2CO-TiCI4
" In atomic units. Table 11. Relative Energies" and Number of Negative Force
Chart I
Constants* for the Stationary Points of the H2CO-TiCI4 System energy structurec H W l HW2 3-21G MIDI-3 DZ N A1 0.0 0.0 0.0 0.0 0.0 0 A2 1.5 1.5 1.5 0 A3 1.8 1.8 1.6 1 A4 1.7 1 1 El 6.2 6.5 5.6 10.0 6.0 E2 11.3 11.7 10.6 3 E3 8.0 8.3 7.6 2 "In kilocalories/mole. b N , computed with the 3-21G basis set. 'See Chart I.
Method of Calculation The molecular geometries of formaldehyde, titanium tetrachloride, and the studied complexes have been fully optimized through ab initio SCF-MO calculations. The computations have been carried out using the 3-21G22and MIDI-323 basis sets. The MIDI-3 basis set for Ti has been increased with a Gaussian p function of exponent 0.080.23 For Ti and CI, the effective core potentials (ECP) of Hay and WadtZ4 have also been used to replace the internal electrons. For the valence shell of Ti two different contractions have been used: a 2s2p2d contraction, denoted by HW1, and a 2s2p3d contraction, denoted by HW2. In both cases a double-r contraction has been used for the valence shell of CI, while 3-21G has been used for H , C, and 0. The energies of the most relevant 3-21G structures have also been calculated with a double-t basis set (DZ). The basis set used for Ti is that of W a c h t e r ~ with , ~ ~ the addition of two Gaussian p functions of exponents 0.03 and 0.09.23 For H , C, 0,and C1 the basis sets of Dunning and Hay have been used.26 For these calculations electron correlation has been taken into account through the third-order Mdler-Plesset perturbation theory (MP3).26 The calculations have been carried out using the G A U S S I A N - Band ~~~ G A M E S S ~programs. ~
B
/
H A2
A1
CI IZ
CI
IZ
0
I
\
C
B
'CJ
H H
A3
A4
CII
Results and Discussion As we have discussed in the introduction, TiC14 and formaldehyde can form 1:1 and 2:1 complexes. X-ray diffraction structures suggest that in some cases a dimerization of the 1:l
cl;
(22) (a) Binkley, J. S.; Pople, J. A.; Hehre, W. J. J. Am. Chem. Soc. 1980, 10.2, 939-947. (b) Gordon, M. S.; Binkley, J. S.; Pople, J. A,; Pietro, W. J.; Hehre, W. J. J . Am. Chem. Soc. 1982, 104, 2797-2803. (c) Dobbs, K. D.; Hehre, W. J. J. Comput. Chem. 1986, 7, 359-378. (23) Huzinaga, S.; Andzelm, J.; Klobulowski, M.; Radzio-Andzelm, E.; Sakai, Y . ;Tatewaki, H. Gaussian Basis Sets f o r Molecular Calculations;
E3
Elsevier: Amsterdam, 1984. (24) Wadt, W. R.; Hay, P. J. J . Chem. Phys. 1985,82, 284-298. (25) Wachters, A. J. H. J . Chem. Phys. 1970, 5.2, 1033. (26) Dunning, T. H.; Hay, P. J. In Methods of Electronic Structures Theory; Schaeffer, H. F., 111, Ed.; Plenum Press: New York, 1977; Chapter 1. (27) Pople, J. A.; Seeger, R.; Krishnan, R. Int. J . Quantum Chem., Symp. 1977, 1 1 , 149. (28) Frisch, M. J.; Binkley, J. S.; Schlegel, H. B.; Raghavachari, K.; Melius, C. F.; Martin, R. L.; Stewart, J. J. P.; Bobrowicz, F. W.; Rohlfing, R. M.; Kahn, L. R.; DeFrees, D. J.; Seeger, R.; Whiteside, R. L.; Fox,D. J.; Fleuder, E. M.; Pople, J. A. GAUSSIAN-86; Carnegie-Mellon Quantum Chemistry Publishing Unit: Pittsburgh, PA, 1984. (29) Schmidt, M. W.; Boatz, J. A.; Baldridge, K. K.; Koseki, S.; Gordon, M. S.; Elbert, S. T.; Lam, B. Quantum Chem. Program Exch. Bull. 1987, 7 , 115.
H
E2
complex has also to be considered.'Oa,dThese processes are summarized in Scheme 1. We will first present the results corresponding to the H2COTiC14complex. The formation of the (H2C0)2-TiC14 complex and the dimerization of the 1:l complex will be discussed in the following two sections. Finally, a comparative analysis will be done. H2CO-TiCI4 Complex. We have considered several possible structures for the H2CO-TiC14 complex. The geometry optimization has led to the structures represented in Chart I, all of them corresponding to stationary points in the potential energy surface of the system. Table I presents the energies of these
J . Am. Chem. Soc.. Vol. 114, No. 11, 1992 4359
Complexes between H 2 C 0 and Tiel4 Scheme I1
Table 111. Computed Formation Energy of the H2CO-TiCI, ComDlex hE AE level of calcn (kcal/mol) level of calcn (kcal/mol) HF/HWl -20.9 HF/MIDI-3 -25.1 HF/HW2 -20.1 HF/DZ -18.4 HF/3-21G -26.6 MP3/DZ -1 3.7
OCH, W
I
El
AI
c'l
CI
\-,/ AI'
structures computed with different basis sets, along with those corresponding to H2C0and TiCI4. One can see that A1 is the most stable structure in all cases. Table I1 presents the energies of all these structures relative to AI as well as the number of negative force constants corresponding to the 3-21G structures. All the structures can be considered as distorted trigonal bipyramids. The formaldehyde molecule is placed in the axis of the bipyramid in A l , A2, A3, and A4 and in the equatorial plane in El, E2, and E3. All these structures present C,symmetry except El and E2, which have C, symmetry. Only AI and A2 structures are energy minima of the potential energy surface, i.e., they have no negative force constants. In both cases formaldehyde presents a bent mode of coordination, syn with respect to the in-plane C1 atom in A1 and anti A2. A4 corresponds to a saddle point of the potential energy surface and can be asscciated with the transition state linking AI and A2. A3 is also a transition state, corresponding to the rearrangement from AI to an analogous structure in which the formaldehyde molecule would be syn with respect to one of the out-of-plane C1 atoms of TiC14. All these processes involve very low energy barriers, thus indicating that such rearrangements are feasible. Moreover, the low energy difference between A3 and A4 indicates that rotation of the H 2 C 0 moiety is almost free. No energy minimum corresponding to a structure in which H2C0 is placed in an equatorial position has been found. The most stable equatorial structure, El,is actually a saddle point of the potential energy surface. An examination of the atomic displacements corresponding to the force constant matrix eigenvector associated with the negative force constant indicates that this structure corresponds to the transition state of an AI AI' rearrangement. As a matter of fact, one can envisage two successive Berry pseudo rotation^^^ connecting A1 with an analogous structure Al' through the E l structure, as indicated in Scheme 11. All along the path connecting both minima, the Ti, 0, and C1, atoms are kept in the plane of the paper. These results show that rearrangements from the most stable structure, A l , can take place easily, with energy barriers lower than 10 kcal/mol. This nonrigidity is normally observed in five-coordinate m~lecules.~'The different basis sets lead to similar results, the only appreciable discrepancy being the MIDI-3 value corresponding to the E l structure. The results obtained with the 3-21G basis set are very similar to those obtained with HWl and HW2, in which ECP are used. In these cases, the use of a double-!: -+
(30) (a) Berry, R. S.J. Chem. Phys. 1960, 32, 923-938. (b) Muetterties, E. L. J. Am. Chem. SOC.1969, 91, 1636-1643. (31) (a) Ugi, A.; Marquarding, D.; Klusacek. H.; Gillespie, P. Acc. Chem. Res. 1971, 4, 288-296. (b) Holmes, R. R. Acc. Chem. Res. 1972.5, 296-303. (32) Morino, Y.;Uehara, H. J. J. Chem. Phys. 1966, 45, 4543.
Table IV. Geometry of the TiCL Molecule basis set RT,
